Revert "tmpfs: add support for multigrain timestamps"

This reverts commit d48c339.

Users reported regressions due to enabling multi-grained timestamps
unconditionally. As no clear consensus on a solution has come up and the
discussion has gone back to the drawing board revert the infrastructure
changes for. If it isn't code that's here to stay, make it go away.

Message-ID: <20230920-keine-eile-c9755b5825db@brauner>
Acked-by: Jan Kara <jack@suse.cz>
Acked-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

mm/shmem.c

@@ -4586,7 +4586,7 @@ static struct file_system_type shmem_fs_type = {
 #endif
 	.kill_sb	= kill_litter_super,
 #ifdef CONFIG_SHMEM
-	.fs_flags	= FS_USERNS_MOUNT | FS_ALLOW_IDMAP | FS_MGTIME,
+	.fs_flags	= FS_USERNS_MOUNT | FS_ALLOW_IDMAP,
 #else
 	.fs_flags	= FS_USERNS_MOUNT,
 #endif